xa0053412 dosimeter characteristics and ......xa0053412 dosimeter characteristics and service...

XA0053412DOSIMETER CHARACTERISTICS AND SERVICEPERFORMANCE REQUIREMENTS

P. AMBROSIPhysikalisch Technische Bundesanstalt,Braunschweig, Germany

D.T. BARTLETTNational Radiological Protection Board,Chilton, United Kingdom

Abstract

The requirements for personal dosimeters and dosimetry services given by ICRP 26, ICRP 35, ICRP 60 and ICRP 75 aresummarised and compared with the requirements given in relevant international standards. Most standards could be mademore relevant to actual workplace conditions. In some standards, the required tests of energy and angular dependence of theresponse are not sufficient, or requirements on overall uncertainty are lacking.

1. INTRODUCTION

World-wide, there are many standards covering requirements for personal dosimeters anddosimetry services. This paper gives an overview of those standards which are either inde-pendent of the measurement quantity, or are written to be used with the new quantities Hp(l0)and //p(0,07). In the following only the new quantity Hp(l0) and photon radiation will beconsidered.

2. GENERAL RADIATION PROTECTION REQUIREMENTS

2.1. ICRP Recommendations 26, 35, 60 and 75

The basis for all requirements in the field of radiation protection is given by the InternationalCommission on Radiation Protection (ICRP).

In Publication 26 [1] in paragraph (104) the Commission recommends a limit for the annualdose-equivalent [The remarks in square brackets are given by the authors.]:

(104) For stochastic effects the Commission's recommended dose limitation is based on theprinciple that the risk should be equal whether the whole body is irradiated uniformly orwhether there is non-uniform irradiation. This condition will be met if... the recommendedannual dose-equivalent limit for uniform irradiation of the whole body... [is] 50 mSv (5 rem).

In Publication 35 [2] the concept of 'Recording Level' is introduced in paragraph (18) and the'Accuracy Required in Routine Monitoring' is given in paragraph (109).

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(18) The recording level is a formally defined value for dose equivalent or intake above whicha result from a monitoring program is of sufficient interest to be worth keeping. TheCommission has recommended that the recording level for individual monitoring should bebased on one-tenth of that fraction of the annual limit corresponding to the period of time towhich the individual monitoring measurement refers...

(109) The uncertainties acceptable in routine monitoring for external radiation should besomewhat less than the investigation level and can best be expressed in relation to theestimates of the annual deep and shallow dose-equivalent indices [now taken to be //p(10) and//p(0.07)] that are measured. The uncertainty in the measurement of the annual value of thesequantities (or of the upper limits if a cautious interpretation is being conducted) should bereduced as far as reasonable achievable. If these quantities are of the order of the relevantannual limits, the uncertainties should not exceed a factor of 1.5 at the 95% confidence level.Where they amount to less than 10 mSv an uncertainty of a factor of 2 at the 95% confidencelevel is acceptable. This uncertainty includes errors due to variations in the dosimeterssensitivity with incident energy and direction of incidence as well as intrinsic errors in thedosimeter and its calibration. It does not include uncertainties in deriving tissue or organdose equivalents from the dosimeter results.

In Publication 60 [3] earlier concepts, relevant to matters of concern here, are mostly retained.In paragraph (257) the reference levels are explained and in paragraph (271) uncertainties aregiven. In paragraph (S25) the dose limits are summarised:

(257) It is often helpful in the management of operations to establish values of measuredquantities above which some specified action or decision should be taken. These values aregenerally called reference levels. They include recording levels, above which a result shouldbe recorded, lower values being ignored; investigation levels, above which the cause or theimplication of the result should be examined; and intervention levels, above which someremedial action should be considered. The use of these levels can avoid unnecessary orunproductive work and can help in the effective deployment of resources. If recording levelsare used, the fact that no unrecorded results exceeded the recording level should be madeclear.

(271) In practice, it is usually possible without great difficulty to achieve an accuracy ofabout 10% at the 95% confidence level for measurements of radiation fields in goodlaboratory conditions. In the workplace, where the energy and the orientation of the radiationfield are rarely known, uncertainties by a factor of 1.5 will not be unusual in the estimation ofthe annual doses from the external exposure of the individual workers. In view of the otheruncertainties this factor is acceptable...

(S25) The Commission recommends a limit on effective dose of 20 mSv per year, averagedover 5 years (100 mSv in 5 years), with the further provision that the effective dose should notexceed 50 mSv in any single year. The 5-year period would have to be defined by theregulatory agency, e.g. as discrete 5-year calendar periods. The Commission would notexpect the period to be introduced and then applied retrospectively. It is implicit in theserecommended dose limits that the dose constraint for optimisation should not exceed 20 mSvin a year.

In Publication 75 [4], the revision of Publication 35, ICRP states in paragraphs (229), (230)Table 2, (232), and (233), and in (249), (250) and (251) the following:

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The Use of Reference Levels

(229) Reference levels are values of measured quantities above which some specified actionor decision should be taken. They include recording levels, above which a result should berecorded, lower values being ignored; investigation levels, above which the cause or theimplications of the result should be examined; intervention levels, above which some remedialaction should be considered; and, more generally, action levels above which some specifiedaction should be taken. ...

(230) Table 2: [The] Recording level [is] set by operating management or nationalauthority, [it] allows records to exclude trivial information, [it is] advisory but should beapplied consistently, [it] applies principally to occupational exposure with particularreference to monitoring of individuals and workplaces.

(232) The Commission now considers that the recording level for individual monitoringshould be derived from the duration of the monitoring period and an annual effective dose ofno lower than 1 mSv or an annual equivalent dose of about 10% of the relevant dose limit. ...

(233) In practice, little use is made of recording levels in individual monitoring for externalexposure because the measured dose is usually entered directly as a measure of the effectivedose. The minimum level of detection should then be used as the recording level with resultsbelow that level being deemed to be zero. However, the recording level is useful in definingthe low dose requirements of dosimeters; it can be used as the basis for defining performancerequirements....

Accuracy

(249) The errors in the use of monitoring to provide estimates of individual doses and intakeslie partly in the measurement and partly in the models linking the measured and the requiredquantities. The errors contributing to the overall uncertainty may be regarded as falling intoat least four broad categories:

(a) random errors in the measurement, e.g. counting statistics,

(b) systematic errors in the measurements, e.g. calibration errors,

(c) errors, mainly systematic, in dosimetric and metabolic models, ...

(d) errors... in the use of the models, ...

(250) Individuals are usually exposed over an extended period and so assessments tend to bebased on a number of measurements made over that period. The use of multiplemeasurements reduces the random errors. For most assessments, the systematic errors inmodelling result in a bias towards over-estimation of the true dose.

(251) The Commission has noted that, in practice, it is usually possible to achieve an accuracyof about 10% at the 95% confidence level for measurements of radiation fields in goodlaboratory conditions (Paragraph 271, Publication 60). In the workplace, where the energyspectrum and orientation of the radiation field are generally not well known, the uncertaintiesin a measurement made with an individual dosimeter will be significantly greater. ... The

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overall uncertainty at the 95% confidence level in the estimation of effective dose around therelevant dose limit may well be a factor of 1.5 in either direction for photons and may besubstantially greater for neutrons of uncertain energy and for electrons. Greater uncertaintiesare also inevitable at low levels of effective dose for all qualities of radiation.

In the following these requirements are interpreted for the most important case of amonitoring period of one month. The factors given above mean that the value of the quotientHJHX of the measured dose value, Hm, and the conventionally true value, Ht, has firstly to besmaller than or equal to the factors and secondly larger than or equal to the reciprocal of thefactors. The 95% confidence level means that the given requirement must be fulfilled for 19 of20 different measurements. In terms of uncertainties, the recording level is interpreted toallow a 100% relative uncertainty for a true dose value of the recording level itself. Therecording level for individual monitoring should be derived from the duration of themonitoring period. For a monitoring period of one month the recording level is

50 mSv/(1012) = 0.42 mSv, according to ICRP 21/35,20 mSv/(1012) = 0.17 mSv, according to ICRP 35/60,not lower than 1 mSv/12 = 0.085 mSv according to ICRP 60/75.

Thus the following two requirements are drawn from ICRP 26 to ICRP 75, see also Table 1and the broad lines in Figure 1:

1. For a dose value equal to or approaching the annual dose limit, the relation1.5 > HJHx ^ 1/1-5 must be fulfilled for 19 of 20 different measurements.

2. For a dose value less than or equal to Ht, the recording level for monthly monitoring, therelation 2.0 > HJHX > 0.0 must be fulfilled for 19 of 20 different measurements.

These two requirements are represented by the solid bars in Figure 1. They must be linkedtogether in some way. This necessity is indicated by the straight dashed lines in that Figure 1.

TABLE I. REQUIREMENTS GIVEN BY ICRP 26 TO ICRP 75 AND THEIRINTERPRETATION WITH RESPECT TO UNCERTAINTY FOR MONTHLY MONITORING

Dose limit orlevel

ftn>ft,annual limit

Hm<Ht

recordinglevel

Dose value according to

ICRP 26/35 ICRP 35/60 ICRP 60/75

/fa =50mSv

ft = 0.42mSv

Ha =20mSv

ft = 0.17mSv

Ha =20mSv

ft > 0.085mSv

Requirements

1.5 > ft/ft > 1/1.5for 19 of 20 measurements

2.0 > ft/ft > 0.0for 19 of 20 measurements

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2.2. Trumpet curves

The requirements of Table 1 can be met by so-called 'trumpet curves' [5,6]. They are used inmany countries and are also incorporated in a number of standards. If Ho is the equivalent tothe recording level for monthly monitoring, e.g. 0.017 mSv according to ICRP 35/60 or notlower than 0.085 mSv according to ICRP 60/75, then the upper limit of the ratio HJHt isgiven by

= L5 1+Upper Limit

and the lower limit by

2H0+Ht(1)

Lower Limit

_ 1 f, 2H015 I H0+Ht

(2)

These limits, the trumpet curves, are shown as dashed curves in Figure 1 for the twocombinations ICRP 35/60 and ICRP 60/75 given above. They are the basic requirements forperformance testing of dosimetry services and dosimeters. The methods for testing are givenin the Section 3.

1/1 .5-

0 . 5 -

Monthly monitoring• " • • ICRP 60 and ICRP 75

trumpet curve, Ho = 0.17 mSvtrumpet curve, HQ = 0.085 mSv

100 mSv 1000

FIG. 1. Limits for the ratio HJHt for monthly monitoring according to ICRP 60 and ICRP 75 and thetrumpet curves for Ho = 0.17 mSv and Ho = 0.0.085 mSv. (Hm is the^measwed dose value and H,, the

conventionally true value. 95% of all measurements must be within the limits).

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3. REQUIREMENTS FROM INTERNATIONAL STANDARDS

3.1. Relevant standards

Table II gives a list of those relevant international standards for personal monitoring which areeither independent of the measuring quantity or are written to be used with the new quantitiesZ/p(10) and i/p(0,07). In the following the requirements of these standards for Hp(\0) fromphoton radiation will be described and compared in detail with respect to requirements onoverall accuracy, energy and directional dependence, linearity, coefficient of variation,environmental effects, electromagnetic fields and mechanical shock. There are of course addi-tional influence quantities such as chemical vapours, and other types of radiation such as betaor neutron radiation, but these effects are not discussed here. Finally, we give our judgementon the relevance of these standards for actual conditions of use.

The International Electrotechnical Commission (IEC) issues a series of requirements,IEC 1283, IEC 1525 and EEC 1526 (draft), which are intended to be identical for the quantity//p(10) from X, gamma and high energy beta radiation and which should differ only inadditional requirements, either in the validity for neutrons in the case of EEC 1525 or in theadditional quantity Hp(0,07) in the case of the draft of EEC 1526. There are in fact somemarginal differences in the requirements for the quantity Hp(\0) from X, gamma and highenergy beta radiation, but in the following all these requirements are referenced asEEC 1283 series. If in some cases the differences seem important then they are indicated in thetext.

3.2. Overall uncertainty

Methods for calculating the overall uncertainty from component uncertainties measured, forexample, in type tests are given in the 'ISO guide', by ISO and other international bodies [15].It is not the aim of this paper to repeat details of these methods here. Table EH gives anoverview on the requirements on overall accuracy given in the relevant standards.

Comparing the different requirements three problems arise. Firstly, the requirements by ICRP(and consequently the trumpet curves) are asymmetrical (on a linear plot) with respect to theconventionally true value whereas the percentage deviation, which is used in nearly all caseswhere the overall uncertainty is calculated from component uncertainties measured in typetests, is symmetrical. Secondly, some requirements, for example those of ICRP are directedtowards the final dose values assessed by a service which may include a calibration error ornormalisation factor, whereas some requirements concentrate on the type test (performance)characteristics of a dosimeter and do not incorporate calibration errors, for example PTB 95.Thirdly, the confidence level (or the coverage factor according to [15]) is not the same for allstandards. Some standards do not even give any requirement on the overall uncertainty. Inthese cases in Table 3 the overall uncertainty shown is calculated according to the ISO guidewith a coverage factor of two.

The requirements by EUR 73, ISO 14146 draft and IAEA 97 draft essentially follow theICRP 35/60 requirements with asymmetrical limits, the PTB 95 requirements withsymmetrical limits. The trumpet curves were devised to be in accordance with the ICRPrequirements. The requirements of EEC 1066 and EEC 1283 series permit much largeruncertainties than those of ICRP.

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TABLE II. LIST OF RELEVANT INTERNATIONAL STANDARDS FOR PERSONALMONITORING

Abbreviation

ICRP35

ICRP60

ICRP75

EUR 73

ISO 14146 d

IEC 1066

EEC 1283 ser.

IAEA 97 d

PTB95

Standard or requirement

ICRP: General Principles of Monitoring for Radiation Protection ofWorkers. Publication 35, 1982 [2]

ICRP: 1990 Recommendations of the International Commission onRadiological Protection. Publication 60, 1991 [3]

ICRP: General Principles for the Radiation Protection of Workers.Written to update Publication 75, 1997, in press [4]

European Commission: Technical recommendations for monitoringindividuals occupationally exposed to external radiation. EUR 14852EN, 1994 [7]

ISO/DIS 14146: Criteria and performance limits for periodic testing ofexternal individual dosimetry for X and gamma radiations. ISO/TC85/SC2N518,Draftl996[8]

IEC 1066: Thermoluminescence dosimetry systems for personal andenvironmental monitoring. 1991 [9]

DEC 1283: Radiation protection instrumentation - Direct readingpersonal dose equivalent (rate) monitors - X, gamma and high energybeta radiation. 1995 [10]

DEC 1525: Radiation protection instrumentation - X, gamma, highenergy beta and neutron radiations - Direct reading personal doseequivalent and/or dose equivalent rate monitors. 1996 [11]

DEC 45B/162/CDV: Direct reading personal dose equivalent and/ordose equivalent rate monitors for the measurement of personal doseequivalent Hp( 10) andHp(0.07) for X, gamma and beta radiation. Draftof IEC 1526,1996 [12]

IAEA Safety Series: Draft Safety Guide: Assessment of occupationalexposures to external radiation. NENS-12. Revised 6 February, 1997[13]

PTB requirements: Measuring instruments for use in radiationprotection: Individual dosimeters for the measurement of personal doseequivalent Hp(10) andH/0.07), November 1995 [14]

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TABLE III. REQUIREMENTS OF RELEVANT INTERNATIONAL STANDARDS ONOVERALL ACCURACY FOR MONTHLY MONITORING

Standard

ICRP35

ICRP60

ICRP75

EUR 73

ISO 14146 d

IEC 1066

IEC 1283 ser.

IAEA 97 d

PTB95

Requirements on overall accuracy

95% level: 1.5 > HJHt > 1/1.5 for Ht * Ha (Ha = 50 mSv [ICRP 26])

(H^ = 20mSv[ICRP60])

2.0 > HJHt > 0.5 for Ht < 10 mSv [ICRP 26]2.0>HJHt>0 forHt=Htt Ht = HJ 120

1.5 > HJHt ^ 1 /1.5 for Hx « Ht = 20 mSv

95% level: 1.5 > HJHt > 1 /1.5 for Ht« Ha (Wa = 20 mSv [ICRP 60])

2.0 > HJHt Z 0 for Ht =Ht, Ht > 0.085 mSv

95% level: trumpet curve with Ho = H\ 110 (2.0 > HJHt > 0 for Ht = Ho)(HQ is lowest dose required to be measured)Ha - 20 mSv as given by ICRP 60

• /To = 0.17 mSv for monthly monitoring period, H\ =20mSv/12• Ho - 0.08 mSv for two-weekly monitoring period, H\ =20 mSv/24

90% level: trumpet curve {HQ > 0.2 mSv is the lower limit of the doserange specified in the type test)

no requirement(95% level: 1.77 > HJH, > 0.33 Calculated according to ISO guide)

no requirement(95% level: 2.1 > HJH, >0.0 Calculated according to ISO guide)

as EUR 73

92% level: 1 + 0A-t(HJ > HJHmje{> 1 - OA-t(H0 , H0 < 0.2 mSv

Definitions: Hm := measured dose value for the period considered^m,ref '•- measured dose value under reference conditionsHx :- conventional true value of the doseHa := dose limit for the period of one yearHT := recording level for the period of one monthH) := dose limit for the period consideredt/95 := absolute uncertainty ofHm on 95% level

trumpet curve: 1(\ 2™P ) < H m < L 5 f l i H ° 1

20 hft r u m p e t function: t[Ht) - 1 + " ; „ --0- ,

9 Ho + Ht

HQ := lowest dose for which trumpet curve can be used

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3.3. Energy and directional dependence

Table IV shows the requirements on energy and directional dependence. There are significantdifferences between these requirements.

TABLE IV. REQUIREMENTS OF RELEVANT INTERNATIONAL STANDARD ON ENERGYAND DIRECTIONAL DEPENDENCE

Standard Requirements on acceptable uncertainty due toenergy and directional dependence

ICRP35ICRP60ICRP75

No specific requirements, they are

included in total overall uncertainty of a factor of 1.5

at or near dose limits

EUR 73- 1 < 1.96 A (A » 0.16)

E : ISO narrow spectrum series is preferred, no mixturesA : calculated to fulfill overall uncertainty requirement

ISO 14146 d No specific requirements, included in overall uncertaintyE, a : all values from rated range of use, even mixtures

IEC 1066£,0u < 0.3 - / (I := confidence interval « 0.03)

E : 15.8 keV, 30 - 40 keV, 80-100 keV, 137Cs or 60Cono other energies, no mixtures

< 0.15 - / (I := confidence interval » 0.03)

a : 20°, 40°, 60°; no other energies, no mixtures

IEC 1283 ser. R n/R£.0u Cs-137,0u - 1 < 0.30 , E : ISO narrow spectrum series

50 keV to 1.5 MeV, no mixtures (IEC 1526 draft: 20 keV to 1.5 MeV)

- 1 <0.50 and - 1 <0.20

a : 15°, 30°, 45°, 60°, 75°; no other energies, no mixtures(IEC 1526 draft: without 75°)

IAEA97d as EUR 73, but all ISO series can be used

PTB95 and G(Ht) < 0.4t(Ht)

E, a : all values from rated range of use, even mixtures

Definitions: Hm : = measured dose valueHi : = conventional true dose valueR : = response, R = Hm /H,RE, a '• = response at mean energy E and incident angle aG(Hf): = overall uncertainty at the 92% level for the true dose H,

20 HTrumpet function t(Ht) = 1 + — ——°—,

9 Ho + Ht

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The ICRP and ISO 14146 draft have no specific requirements, only the requirement on theoverall uncertainty.

In EUR 73 and IAEA 97 draft, the requirements on energy and directional dependence arecombined. For every radiation quality used for the test the directional dependence isconsidered by calculating the mean value of the response at 0°, 20°, 40° and 60°. Thedeviation of this mean value from unity is limited by a parameter A, which is calculated suchthat the overall uncertainty (for all influence quantities and other parameters like coefficient ofvariation) does not exceed the limits given by the trumpet curves. A is of the order of 0.16. Forthe tests, ISO (EUR 73: narrow only specified) spectrum series are preferred, no mixtures areallowed. Due to the use of the mean value of the response the overall uncertainty can exceedthe limits given by the trumpet curves, if the directional dependence of the response is largeand the monitored person is irradiated mainly from one direction. The limits can also beexceeded by mixed radiation fields or even broad spectra, if an evaluation procedure usingnon-linear algorithms is optimised only for the test radiation fields (see paper on 'WorkplaceFields" [15]).

In IEC 1066, in order to take into account the statistical uncertainty in a test result, theconfidence interval, /, for the test is specified (from experience I is of the order of 0.03).IEC 1066 has separate requirements for the energy dependence of the response and the di-rectional dependence of the response. For the first the deviation from unity must not exceed0.3 - 7 for 4 test energies: 15.8 keV, 30 - 40 keV, 80 - 100 keV and 137Cs or 60Co. No otherenergies and no mixtures are used. The directional dependence of the response is only testedat one energy and four angles: 60 keV and 0°, 20°, 40° and 60°. The deviation of the responsefor 20°, 40° and 60° must not deviate from that at 0° by more than 0.15-7. Due to the limitedextent of the tests the overall uncertainty can exceed the limits given by the trumpet curves.The probability to exceed the limits is larger than for the EUR 73 requirements.

The IEC 1283 series requirements have similarities with the IEC 1066 requirements. Again,separate requirements for the energy dependence of the response and the directionaldependence of the response are given. For the energy dependence the deviation from unitymust not exceed 0.3 for all 8 (EEC 1526 draft: 11) test energies of the ISO series. No mixturesare used. The directional dependence of the response is tested at two energies and six(IEC 1526 draft: five) angles: 60keV plus 137Cs and 0°, 15°, 30°, 45°, 60° and 75°(IEC 1526 draft: without 75°). The deviation of the response for oblique incidence must notdeviate from that at 0° by more than 0.5 for 60 keV and 0.20 for 137Cs. For use in the vicinityof nuclear reactor installations the response at 6 MeV must be between -50% and +100%. Alsofor the IEC 1283 series requirement the overall uncertainty can exceed the limits given by thetrumpet curves.

The PTB 95 requirements on energy and directional dependence are combined. The responsefor every energy and direction of incidence, even any mixture, must not deviate from that atreference conditions by more than about 0.35. This factor depends slightly on the otherperformance characteristics and is adjusted so that the overall uncertainty calculated accordingto the ISO guide with a coverage factor of ^3 does not exceed OAtfHJ. This procedure issimilar to that in EUR 73. The function t(HJ is given in Table 3. It produces a symmetricaltrumpet curve.

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3.4. Linearity and coefficient of variation

Table 5 shows the requirements on linearity and Table 6 those on coefficient of variation.Most standards have no specific requirements, only the requirement on the overall uncertainty.For those standards having specific requirements the differences are not very large.

TABLE V. REQUIREMENTS OF RELEVANT INTERNATIONAL STANDARDS ONLINEARITY

Standard

ICRP35ICRP60ICRP75EUR 73ISO 14146d

EEC 1066

IEC 1283ser.

IAEA 97 d

PTB95

Requirements on Linearity

No specific requirements, included in overall uncertainty

No specific requirements, included in overall uncertaintyThe range Ho < Hx < 1 Sv should be tested

R(Ht) - 1

R(Ht) - 1

< 0.1-7 (/ := confidence interval» 0.03) for 0.1 mSv < Ht < 1 Sv

< 0.15 for the 'value of the relative intrinsic error over the

effective range of measurement'

No specific requirements, included in overall uncertainty. No rated range ofuse

^m a*~^m l n <0.15 for 0.2 mSv < Hx < 1 Sv

(For larger dose values a ratio of 0.25 is allowed)

Definitions: Hm := measured dose valueHx := conventional true dose valueR(HJ := response, R = HmIHx

jRmax := maximum value of the response in the specified rangei?mjn := minimum value of the response in the specified range

The IEC 1066 requires for linearity, that the deviation of the response from unity must notexceed 0.1-7 for the range HQ<HX< 1 Sv. The requirement for the coefficient of variation isthat it must not exceed 0.075-7 for both, a sample of n dosimeters and 10 repeatedmeasurements with the same dosimeter. Again, 7 is the confidence interval for the test.

The IEC 1283 series have a combined requirement for linearity and coefficient of variation,called 'relative intrinsic error'. The deviation of the response from unity must not exceed 0.15for the 'effective range of measurement' for any single measurement.

The PTB 95 requires that the nonlinearity, calculated according to the formula given inTable V, must not exceed 0.15 in the range 0.2 mSv < Hx < 1 Sv. For larger dose values avalue of 0.25 is allowed. For the coefficient of variation a test procedure is given to calculatethis coefficient in such a way that it incorporates the uncertainty due to differences in batchmanufacturing, in build-up or fading due to the time of exposure in the given measuringperiod and its dose dependence. The requirement itself is included in the overall uncertainty.

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TABLE VI. REQUIREMENTS OF RELEVANT INTERNATIONAL STANDARDS FORCOEFFICIENT OF VARIATION

Standard

ICRP35ICRP60ICRP75EUR 73ISO 14146d

EEC 1066

IEC 1283ser.

IAEA 97 d

PTB95

Requirements for coefficient of variation


v(10 mSv) < 0.075 - / (/ := confidence interval« 0.03) fora) a sample of n dosimeters orb) 10 repeated measurements with the same dosimeter

No specific requirements, included in the requirement on linearity


v(Ht) must be measured over the whole dose range for a sample ofdosimeters stored up to the maximum wear period and fulfilloverall uncertainty requirement

Definitions: Hm : = measured dose value

Ht : = conventional true dose value

v (B) := coefficient of variation,v(Ht )=s{Hm)/ Hm

3.5. Environmental effects, electromagnetic fields and mechanical shock

The requirements on climatic effects, light exposure, electromagnetic fields and mechanicalshock dependence are shown in Tables VT to X.

Explicit requirements for these influence quantities are only given by three standards,IEC 1066, EEC 1283 series and PTB 95, all others have included the requirements in theoverall uncertainty.

In EEC 1066 three tests on climatic dependence are prescribed, one at normal temperature(20 °C) and elevated relative humidity (90%), and a second at elevated temperature (50 °C)and normal relative humidity (65%). In both cases the storage time is 30 days and therequirement is that the deviation of the response from unity must not exceed 0.2 - /. The thirdtest is at standard test conditions (18-20 degree C, 50-60% RH), for which the deviation of theresponse must not exceed 5% after 30 days storage, or 10% after 90 days. For the lightdependence one test at bright sunlight (1000 W/m2 with the spectral distribution at sea level,normal incidence and clear sky) is given. The duration is 168 h (7 days) and the requirement isthat the deviation of the response from unity must not exceed 0.1 - /.

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The UV part especially of the spectral distribution must be carefully monitored during the test.For the shock dependence one test is given. After a drop of 1.0 m height on concrete surfacethe deviation of the response from unity must not exceed 0.1 - /. As before, / is the confidenceinterval.

TABLE VII. REQUIREMENTS OF RELEVANT INTERNATIONAL STANDARDS FOREFFECTS OF CLIMATIC CONDITIONS

StandardICRP35ICRP60ICRP75EUR 73ISO 14146 dIEC 1066

IEC 1283 ser.

IAEA 97 dPTB 95

Requirements given for effects due to climatic conditions


Not tested, see type test results

RTr - 1 < 0.2 - / (/ := confidence interval « 0.03) for

a) 30 days storage at T= 20 °C and r = 90% rel. humidityb) 30 days storage at T= 50 °C and r = 65% rel. humidity

* r . 6 5 % / # 2 0 O c 6 5 % - l

RT65%/R o - 1

/VT-«qt / K — 1

<0.2 for - 1 0 ° C < r < 4 0 ° C

< 0.5 for - 20 °C < T< 50 °C (only IEC 1283: -25 °C)

< 0.1 for 40% < r < 90%


- 10°C<T<

< 0.2 for 48 h storage at any combination of

: 40 °C and 10% < r < 90% (&, < 30 g.m"3)Definitions: Hm := measured dose value

Ht := conventional true dose valueR := response, R = Hm /Ht

RT, r '•- response at temperature T and relative humidity rPv, := water vapour density

In IEC 1283 series the temperature dependence and the relative humidity dependence aretested separately. For the temperature two rated ranges of use are given, one from -10°C to40°C with a maximum change of the response of 20% and a second lager one from -20°C(only IEC 1283: -25°C) to 50°C with a maximum change of the response of 50%. For relativehumidity the rated range of use is from 40% to 90% and a maximum change of the responseof 10%. For light dependence no test and no requirement is given. The requiredelectromagnetic field immunity is that for the range of values shown (Table DC), the responsemust not change by more than 10%. Similarly, the response must not change by more than10% if a mechanical shock, a 1.5 m drop on hard wood surface, is applied. Additionalvibration tests are prescribed.

The PTB 95 combines temperature dependence and the humidity dependence and requires thatthe response must not change by more the 20% for any combination out of the two ratedranges of use, for temperature from -10°C to 40°C and for relative humidity from 40% to

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90%. The absolute humidity in these tests is limited to 30 g.m'3 (equivalent at 40°C to arelative humidity of about 60%). The light dependence is limited to a change of the responseof 10% after 48 h storage at bright sunlight of the same spectral distribution as given byIEC 1066. The electromagnetic field immunity requirements are shown in Table IX. There aretwo sets of tests in PTB 95, one following an IEC recommendation (DEC 1000-4-2/3/4/5/6/8/11) and the other set designed to simulate the fields produced by portable digitaltelephones. For both sets of tests, the requirement is that the response must not change bymore than 10%. For mechanical shock the requirement is that after a sinusoidal shock of 1 msduration and 4900 m/s2 amplitude the response must not change by more than 10%. Thisshock is equivalent to a drop of 0.5 m on a concrete surface.

4. RELEVANCE/APPLICABILITY TO WORKPLACE CONDITIONS

The aim of all the relevant standards should be to determine whether the performance of anindividual dosimeter or dosimetry service is good, or at least adequate, in normal routine use.The requirements of the standards should be relevant for actual workplace conditions. Anystandard is a compromise of the views of the originators, influenced by their professionalexperience, and the state of the art of the dosimeters to which the standard should be applied.We give in Table XI our opinion as to the relevance of these standards for workplaceconditions.

The ICRP publications serve as general guidelines and have, therefore, a large relevance, butthey do not give any detailed requirements or test procedures.

The EUR 73 recommendations give much information on the measurement quantities andgive some detailed test procedures, but the requirements for the most important influencequantities, the energy and radiation incidence direction, are not complete (see paragraph 3.3)and for many influence quantities, none are given. The relevance/applicability to workplaceconditions is only medium. However, together with IAEA 97, these recommendations includerequirements for many operational aspects of dosimetry services

The ISO 14146 draft is intended for the routine testing of dosimeters in use by dosimetryservices, and therefore the relevance/applicability to normal conditions of use is large, but atype test should also be specified.

The EEC 1066 is a good standard, in general, which addresses both detectors and readers, butspecifies only four energies for the assessment of the energy response characteristics and thedependence of response on radiation incidence direction is only required to be investigated atone energy. Two dosimeters with the same test results, may have quite different performancein realistic workplace conditions. Therefore, the relevance/applicability to such conditions isconsidered small.

The DEC 1283 series have more energy values than EEC 1066 for testing the influence quantityradiation energy, and specifies at least two energy values for testing radiation incidencedirection, but has much the same deficiencies. We conclude that IEC 1283 series havemedium relevance/applicability to realistic workplace conditions, and note that the requiredvalue for the overall uncertainty is rather large.

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The IAEA 97 Draft has many similarities to EUR 73, and therefore similarrelevance/applicability (medium) to actual conditions of use, but note the useful requirementsgiven for operational aspects of dosimetry services

TABLE Vm. REQUIREMENTS OF RELEVANT INTERNATIONAL STANDARDS FORSENSITIVITY TO LIGHT

Standard

ICRP35

ICRP60

ICRP75

EUR 73

ISO 14146 d

IEC 1066

IEC 1283 ser.

IAEA 97 d

PTB 95

Requirements for sensitivity to light



for 168 h storage

< 0 .1- 7 (/ := confidence interval « 0.03)

at bright sunlight (1000 W.m'2 at sea level)

No test, no requirement


|^Light/-RDark~l

at sea level)

< 0.1 for 48 h storage at bright sunlight (1000 W.m'2

Definitions: Hm := measured dose valueHx := conventional true dose valueR •- response, R = Hm /Ht

-Kught '•= response after specified light exposure-̂ Dark := response after storage in darkness

The PTB 95 requirements give detailed test procedures for almost all influence quantities andplace most importance on satisfying the requirements on overall uncertainty. We consider thatthe relevance/applicability to actual workplace conditions is large.

4.1. List of methods

The best method of performance testing is one which allows the assessment of theperformance of the service for routine measurements in workplace conditions. The servicemust not do any special treatment to the dosimeters to avoid unrepresentative results. Threemethods for performance testing will be explained in the following, the 'blind' test, the'surprise' test and the 'announced' test. According to the legal and local circumstances, otherapproaches may be acceptable.

133

In a 'blind' test the service is not aware of the tests and cannot use selected dosimeters orspecial evaluation procedures for the tests. One approach is the invention of a 'dummycustomer' and controlled irradiation of the dosimeters by a control institute. Normally, anydose above a certain threshold leads to an alert to the authorities, this alert needs to be blockedfor these tests. The largest Netherlands and UK services use a dummy customer for qualityassurance purposes [17]. Another approach is to issue the same person, identified as someonewho gets a non-zero dose, with several (perhaps electronic) dosimeters. In this case themeasurement is done in a real radiation field under workplace conditions, but the value of Ht

is unknown.

TABLE IX. REQUIREMENTS OF RELEVANT INTERNATIONAL STANDARDS FORELECTROMAGNETIC FIELD IMMUNITY

Standard Requirements given for effects due to electromagnetic fields

ICRP35

ICRP60

ICRP75

EUR 73

No specific requirements (included in overall uncertainty)

ISO 14146 d Not tested, see type test results

IEC 1066 No requirements

IEC 1283 ser. Warning if influenced by electromagnetic fieldsIf manufacturer claims insensitivity:

\Rfield/Rref-]- <0.1 forlOV/m 100 kHz to 500 MHzCW-field

1 V/m 500 MHz to 1 GHz CW-E-field60 A/m 50 Hz CW-field6 kV discharge (IEC 1526 draft: 8 keV)

IAEA 97 d No requirements

PTB95 Rfield/Rref-l < 0.1 for the total of all tests,

tests according to IEC 1000-4-2/3/4/5/6/8/11 (8 kV discharge,10 V/m 80 kHz to 1 GHz fields, ±2 kV transients , ±4 kV bursts,10 V 150 kHz to 80 MHz line voltage, 30 A/m 50 Hz field)20 V/m 0.9 GHz 100% AM/200 Hz/50% and15 V/m 1.8 GHz 100% AM/200 Hz/50%(equivalent to Handy at 30 cm distance)

Definitions: Hm

RAfield

:= measured dose value:= conventional true dose value:= response, R = Hm /Ht

:= response after exposure to specified field:= response after storage without shock

134

In a 'surprise' test the service is aware of the tests but does not know the actual test date inadvance (e. g. once a year). The service may use selected dosimeters but cannot use specialevaluation procedures. The control institute receives regularly a fixed number of dosimeters.The dosimeters are irradiated. Without prior notice, an official of the verification officesubmits, in person, the irradiated dosimeters to the service. The official observes theevaluation, which should follow written quality assured procedures, and passes the resultsback to the control institute. This method avoids the high dose alert to the authorities.

In an 'announced' test the service is aware of the tests and may use selected dosimeters andspecial evaluation procedures. The control institute asks the service to send the dosimeters toit and irradiates them. Then the dosimeters are sent back to the service for evaluation. The UKregulatory body (HSE) and many international (including IAEA) intercomparisons are of thistype.

TABLE X. REQUIREMENTS OF RELEVANT INTERNATIONAL STANDARDS FOREFFECTS OF MECHANICAL SHOCK

Standard

ICRP35

ICRP60

ICRP75

EUR 73

ISO 14146 d

IEC 1066

IEC 1283 ser.

IAEA 97 d

PTB95

Definitions:

Requirements given for effects of mechanical shock



after 1.0

1 ^Shock/-fW ~ 1(additional vibra

< 0 .1-1 (/ := confidence interval« 0.03)

m drop on concrete surface

< 0.1 after 1.5 m drop on hard wood surface

tion test)


1 ^Shock/-^ef ~ ^(equivalent to 0.

< 0.1 after sinusoidal shocks, 1 ms, 4900 m/s2

5 m drop on concrete surface)

Hm := measured dose valueHx :- conventional true dose valueR := response, R = Hm /Ht

•Kshock := response after specified shock exposureRm '•= response after storage without shock

135

TABLE XI. CONDITIONS OF USE OF DOSIMETERS AND DOSIMETRY SERVICES

Standard

ICRP35ICRP60ICRP75EUR 73

ISO 14146 d

IEC 1066

IEC 1283 ser.

IAEA 97 d

PTB 95

Relevance/applicability of the standard to workplace conditions

Large: General guidance, no test procedures given

Medium: Dependent on evaluation procedure and angular dependenceof the response. Operational aspects of service included.

Large: But 10 tested dosimeters per year are only sufficient if a type testhas been performed in advance

Small: No overall uncertainty, only 4 test energies, the angular depend-ence is tested at only one energy, strongly dependent on evaluationprocedure

Medium: No overall uncertainty, no mixture of test energies, theangular dependence is tested at only 2 energies, strongly dependent onevaluation procedure. Required overall uncertainty large

Medium: Dependent on evaluation procedure and angular dependenceof the response. Operational aspects of service included.

Large: Detailed test procedures given

5. METHODS OF PERFORMANCE TESTING

5.1. Example

The German performance tests are of the surprise test type. The method of the performancetest is illustrated in Figure 2. Every service is tested once a year with all its types ofdosimeters. The Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig is the controlinstitute. Therefore, the PTB irradiates every year about 200 dosimeters of the 6 Germanservices for this test. The dose varies from 0.2 mSv to 10 Sv, the radiation mean energy from20keV to 1250 keV and the angle of radiation incidence from 0° to ±45°. Mixtures ofradiation qualities and angles of radiation incidence are frequently used.

The results for the years 1990 to 1995 are shown in Figure 3. All services fulfilled therequirements. The difference in performance between film, TL and RPL dosimeters isminimal. Similar results have been obtained in other countries [6]. All these results indicatethat the ICRP requirements are practical and can be fulfilled in routine monitoring.

6. OVERVIEW OF SERVICE PERFORMANCE REQUIREMENTS

Some service performance requirements are given by the ICRP, more requirements are onlygiven in two standards, EUR 73 and IAEA 97 draft. Both give a lot of requirements andrecommendations which are similar in many aspects. In this overview it is only possible to listsome headlines of these two standards; this is done in Table XII.

136

Dosimetry service

evaluate ixjifeis evening

FIG. 2. Method of the regular surprise tests conducted in Germany. See text for details.

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TABLE XII. SERVICE PERFORMANCE REQUIREMENTS AND RECOMMENDATIONS INEUR 73 AND IAEA 97 DRAFT

Standard

EUR 73

IAEA 97 d

Requirements given for

• Dose record data

• Recording and reporting levels

• Reporting of dose information

• Setting up a dose record and information system

• Organisational structure and personnel

• Laboratory accommodation and environment

• Scientific research

• Quality assurance

• Dose record keeping for individual monitoring

• Record keeping for workplace monitoring

• Quality assurance requirements

• Documentation of methods, procedures and test results

• Quality awareness and training of personnel

• Acceptance testing of newly supplied materials

• The laboratory accommodation and environment

• Maintenance and testing of equipment, materials and processes

• Verification of calibration facilities

• Testing the overall performance of the system

138

i l l nri 11 11II I I

1990-1996

o

RIrn 13of420outTLD 1of250outPLD 3of29Dout

0.08510

i i i i 1111

100 1000 rrS/10000.17 n

FIG. 3. Results of the regular surprise tests conducted in Germany for film, TL and RPL dosimeters ofthe years 1990 to 1995. The solid lines are the trumpet curves for Ho = 0.17 mS\, the dashed ones

those for Ho = 0.085 mSv. Hm is the measured dose value andHb the conventionally true value. 95%of all measurements must be within the limits

REFERENCES

[1] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION.Recommendations of the International Commission on Radiological Protection. ICRPPublication 26, Pergamon Press, Oxford (1977).

[2] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION. GeneralPrinciples of Monitoring for Radiation Protection of Workers. ICRP Publication 35,Annals of ICRP 9, Nr.4, Pergamon Press, Oxford (1982).

[3] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION. 1990Recommendations of the International Commission on Radiological Protection. ICRPPublication 60, Annals of ICRP 21, Nr.1-3, Pergamon Press, Oxford (1991).

[4] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION. GeneralPrinciples for the Radiation Protection of Workers. ICRP Publication 75, written toupdate and replace ICRP Publication 35 [2], (1997).

[5] BOHM, J., AMBROSI, P., Mandatory Type Tests of Solid State Dosimetry Systems asan Appropriate Aid to Quality Assurance in Individual Monitoring. Rad. Prot. Dosim.34, 1990, 123-126.

139

[6] BOHM, 1, LEBEDEV, V. N., MCDONALD, J. C , Performance testing of DosimetryServices and its Regulatory Aspects. Rad. Prot. Dosim., 54, 1994, S. 311-319.

[7] EUROPEAN COMMISSION, Technical recommendations for monitoring individualsoccupationally exposed to external radiation. EUR 14852 EN, (1994).

[8] ISO/DIS 14146, Criteria and performance limits for periodic testing of externalindividual dosimetry for X and gamma radiations. ISO/TC 85/SC 2 N 518, (1996).

[9] INTERNATIONAL ELECTROTECHNICAL COMMISSION, Thermohiminescencedosimetry systems for personal and environmental monitoring. IEC 1066,1991-12.

[10] INTERNATIONAL ELECTROTECHNICAL COMMISSION, Radiation protectioninstrumentation - Direct reading personal dose equivalent (rate) monitors - X, gammaand high energy beta radiation. IEC 1283,1995-02.

[11] INTERNATIONAL ELECTROTECHNICAL COMMISSION, Radiation protectioninstrumentation - X, gamma, high energy beta and neutron radiations - Direct readingpersonal dose equivalent and/or dose equivalent rate monitors. IEC 1525,1996-09

[12] INTERNATIONAL ELECTROTECHNICAL COMMISSION, Direct reading personaldose equivalent and/or dose equivalent rate monitors for the measurement of personaldose equivalent Hp(10) and Hp(0.07) for X, gamma and beta radiation. 45B/162/CDVDraft of IEC 1526, 1996.

[13] INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of OccupationalExposures to External Radiation. Safety Series, Draft Safety Guide, NENS-12, Revised6 February, Vienna, 1997.

[14] PHYSIKALISCH-TECHNISCHE BUNDESANSTALT, Measuring instruments for usein radiation protection, Individual dosimeters for the measurement of personal doseequivalent Hp(10) and Hp(0.07), November 1995. (an unofficial English translation isavailable from Physikalisch-Technische Bundesanstalt, Fachlabor 6.51,Bundesallee 100, D-38116 Braunschweig).

[15] INTERNATIONAL ORGANISATION FOR STANDARDISATION, Guide to theExpression of Uncertainty in Measurement, ISO, Geneva, (1993).

[16] BURGESS P., BARTLETT D., AMBROSI P., Workplace fields, this publication.

[17] VAN DIJK, T.WE., JULIUS, H. W., Dose thresholds and quality assessment bystatistical analysis of routine individual monitoring TLD data. Rad. Prot. Dosim., 66,(1994), 17-22.

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